Honeycomb stuctural bodies

ABSTRACT

A honeycomb structural body including an outermost peripheral wall, and partition walls axially defining a number of through holes inside the outermost peripheral wall. The honeycomb structural body is bent around at least one line located orthogonally to an extending direction of the through holes, wherein L1/L2≧0.8, and R≧100 mm, in which L1 is an axial length of a longest through hole among through holes located in an outer portion of the honeycomb structural body, L2 is an axial length of a shortest through hole among through holes located in an inner portion of the honeycomb structural body, and R is a radius of curvature of a center line of the honeycomb structural body defined by continuously connecting centroids of said outermost peripheral wall of the honeycomb structural body in respective planes orthogonal to the extending direction of the through holes thereof. The outer and inner portions of the honeycomb structural body are located outside and inside a plane, respectively, passing the center line of the honeycomb structural body and always extending in parallel to the at least one line around which the honeycomb structural body is bent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to curved honeycomb structural bodies.

2. Related Art Statement

Heretofore, honeycomb structural bodies have been produced by extrusion,or by corrugating a sheet and coiling it together with a flat sheet in arolled fashion, or by forming a number of small projections in ametallic sheet in a scattered state through pressing and coiling it in arolled fashion. These honeycomb structural bodies have a number ofstraight-line through holes.

When the conventional honeycomb structural bodies are used as catalystcarriers for the purification of exhaust gases from internal combustionengines in automobiles, there occur the following problems.

1 Since there is a limitation on a fitting site, it is impossible toinstall the catalyst carrier in a location having an optimum temperaturecondition as considered from the standpoint of high temperaturedurability and purification efficiency of the catalyst.

2 Since the flow rate of the exhaust gas at the outer peripheral portionof the honeycomb structural body is smaller than that at the centralportion thereof, a majority of the exhaust gas is purified in thecentral portion of the catalyst. Therefore, it cannot be said that theouter peripheral portion of the honeycomb structural body fullyfunctions as the catalyst, which means poorer purification performancefor the same volume of the catalyst.

SUMMARY OF THE INVENTION

It is an object of the present invention to satisfy recent demands forthe honeycomb structural bodies, and to provide catalyst-carryinghoneycomb structural bodies having excellent purification efficiency ofexhaust gases, which can be each arranged in a free location in a narrowspace inside an engine room.

In order to accomplish the above object, the honeycomb structural bodyaccording to the present invention is characterized by a honeycombstructural body including an outermost peripheral shell or wall, andpartition walls by which a number of through holes extending in an axialdirection of the honeycomb structural body are defined inside theoutermost peripheral wall. The honeycomb structural body is bent aroundat least one line located in a direction orthogonal to an extendingdirection of said through holes being perpendicular to a plane passing acenter line of the honeycomb structural body. The center line beingdefined by continuously connecting centroids of said outermostperipheral wall of the honeycomb structural body in respective planesorthogonal to the extending direction of the through holes thereof. Inthe honeycomb structural body L1/L2 is no less than 0.8, and R is notless than 100 mm, in which L1 is an axial length of a longest throughhole among through holes located in an outer portion of the honeycombstructural body, L2 is an axial length of a shortest through hole amongthrough holes located in an inner portion of the honeycomb structuralbody, and R is a radius of curvature of said center line of thehoneycomb structural body. The outer and inner portions of the honeycombstructural body are located outside and inside a plane, respectively,said plane passing said center line of the honeycomb structural body andalways extending in parallel to said at least one line around which thehoneycomb structural body is bent. The axial length of the through holeis a length of the through hole measured along a longitudinal centralaxis.

Since the honeycomb structural body of the present invention is bent,the honeycomb structural body can be mounted in a narrow space onfitting, which enlarges fitting latitude. Since the flow rate of theexhaust gases increases in a portion of the honeycomb structural bodypositioned on an outer peripheral side as viewed in a curved direction,the exhaust gases fully contact the catalyst to enhance the purificationefficiency of the exhaust gases in the outer peripheral side of thehoneycomb structural body as viewed in the curved direction.

When the ratio of L1/L2 is not less than 0.8 as defined above, thepurification performance for the exhaust gases is improved.Particularly, it was found out that when the L1/L2 ratio is not lessthan 1.2, the exhaust gas purification performance is largely improved.

When the radius R of curvature of the honeycomb structural body is notless than 100 mm as recited above, pressure loss of the honeycombstructural body does not almost increase as compared with theconventional ones, which does not lead to deterioration in the engineperformance such as reduction in outputs of the engine.

According to the honeycomb structural bodies of the present invention,the following are preferred.

1 The center line possess at least two different radii R of curvature.The centers of curves bent at such at least two radii of curvature maybe located on the same side as viewed relative to the plane passing thecenter line of the honeycomb structural body, or may be located ondifferent sides.

2 The honeycomb structural body includes a straightline portion in whichsaid through holes are not bent is provided at least one location at anend portion of the honeycomb structural body or at a portion other thansaid end portion.

3 The honeycomb structural body is made of a ceramic material.

4 A catalyst is carried onto inner walls defining the through holes.

5 The partition walls extend in orthogonal directions as viewed insection at right angles to said extending direction of said throughholes, thereby defining two orthogonal axes as viewed in section, andsaid at least one line is parallel to one of said two orthogonal axes.

6 The sectional shape of the honeycomb structural body as viewed insection orthogonal to said extending direction of the through holes isone selecting from the group consisting of a circular shape, anelliptical shape, an oval shape, a square shape, a rectangular shape andtriangular shape.

These and other objects, features and advantages of the invention willbe appreciated by the skilled person in the art to which the inventionpertains, when taken in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to theattached drawings, wherein:

FIG. 1 is a schematic view for illustrating a state in which a honeycombstructural body according to the present invention is mounted in acatalyst unit in an engine room inside a vehicle;

FIG. 2 is a perspective view for illustrating a first embodiment of thehoneycomb structural body according to the present invention;

FIG. 3 is a perspective view for illustrating a variety of embodimentsof the honeycomb structural bodies according to the present invention asviewed in section cut by a plane perpendicular to a line around whichthe honeycomb structural body is bent;

FIG. 4 is a perspective view for illustrating a honeycomb structuralbody with an end face at a line B--B in FIG. 3;

FIG. 5 is a perspective view for illustrating a honeycomb structuralbody with an end face at a line C--C in FIG. 3;

FIG. 6 is a perspective view for illustrating a honeycomb structuralbody with an end face at a line D--D in FIG. 3;

FIGS. 7(a) through 7(f) are sectional views for schematicallyillustrating variations of outermost peripheral walls of the honeycombstructural bodies according to the present invention;

FIGS. 8(a) through 8(d) are schematic views for illustrating variationsof the shapes of the honeycomb structural bodies according to thepresent invention;

FIGS. 9(a) through 9(d) are schematic views for illustrating furthervariations of the shapes of the honeycomb structural bodies according tothe present invention;

FIG. 10 is a running pattern of an automobile with an engine having adisplacement of 2000 cc in Experiment 1;

FIG. 11 is a characteristic graph showing the relation between emissionamounts of CO, HC and NOx in Experiment 1 of the present invention andthe ratio L1/L2 in length of the longest through hole and the shortestthrough hole; and

FIG. 12 is a characteristic diagram showing the relation between thepressure loss and the radius of the curvature of the curved honeycombstructural body.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained in more detail with reference toembodiments shown in the attached drawings.

In FIG. 1 is shown an example in which a curved honeycomb structuralbody according to the present invention is applied to a rearwheel-driven type passenger car in which an engine is mounted on a frontside.

Inside an engine room 1 is mounted an engine body 2. To an exhaustmanifold 3 in an exhaust system for the engine body 2 is connected anexhaust pipe 4, which is connected to an exhaust port 13 through acatalyst unit 5, a flexible joint 8, and a silencer 10 under a floor ofa vehicle body. The upper portion of the engine body 2 inside the engineroom 1 is covered with a bonnet 18, and a front grill 15 is formed at afront side under bonnet 18. A fan 16 and a radiator 17 are mounted on arear side of the front grill 15. Between the exhaust manifold 3 and thecatalyst unit 5 are fitted an air feed port 20 for feeding a secondaryair into the exhaust pipe 4 as well as an exhaust gas temperature sensor21.

The above catalyst unit 5 is constituted by a catalyst carrier 6 and ametallic casing 7 elastically holding the catalyst carrier 6. As shownin FIG. 1, the catalyst carrier 6 has a curved shape. This catalystcarrier 6 includes a honeycomb structural body 30 for carrying acatalyst as shown in FIG. 2 as well as a catalyst (not shown) carriedonto the surface of the honeycomb structural body.

As shown in FIG. 2, the honeycomb structural body 30 is specificallyconstituted in an elliptical shape as viewed in cross section, and anelliptical-section and elongate outermost wall 33 extends along theouter periphery of the honeycomb structural body having the ellipticalsectional shape. Inside the outermost wall 33 are formed a number ofthrough holes 35 by inner walls or partition walls, which extend andcommunicate between one end face 37(A) to the other 39(E) substantiallyin parallel to a direction in which the outermost wall longitudinallyextends. Curved passages are constituted along the curved shape of thehoneycomb structural body by through holes 35, and the cross sectionalarea of every through hole 35 is substantially constant excluding those35a located adjacent to the outermost wall 33.

A number of the through holes (curved passages) 35 are formed by innerwalls 40 and inner walls 42 which extend in major and minor axes(radial) directions of the ellipse, respectively, and cross in a latticefashion. As shown in FIG. 2, the inner walls 40 and the inner walls 42are bent in a direction toward a central line of curving, and the curvedpassages 35 defined by the crossing inner walls 40 and 42 extend inparallel along the curving direction, and penetrate the honeycombstructural body from the one end face 37(A) to the other 39(E). Thethickness of each of the inner walls 42 extending in the radialdirection is constant (tx), and that of each of the inner walls 40extending in the main axis direction of the ellipse is constant (ty).

If the radius R of curvature of the through hole or through holeslocated on the innermost side of the honeycomb structural body as viewedin a curved direction is too great, the intended advantageous merit thatthe honeycomb structural body can be fitted in a narrow spacedisappears. Thus, it is practically preferable that the radius R ofcurvature of the honeycomb structural body is not more than 500 mm.

FIG. 3 schematically illustrates a variety of honeycomb structuralbodies according to the present invention, in which the positions of theopposite end faces of the honeycomb structural body 30 are shown. In afirst embodiment, one end face 37 is located at a section A--A, and theother 39 is at a section E--E. In the following, embodiments with anA--A end face, a B--B end face, a C--C end face or a D--D end face willbe explained.

(1) A--A end face

According to the first embodiment, the honeycomb structural body 30 iscircular in section around a curving center line (O), and the end faces37 and 39 are formed with flat planes passing the center (O) (a centerline) of the curving center line and crossing the through holes of thehoneycomb structural body at right angles. Therefore, when the oppositeends of the through holes 35 of the honeycomb structural body 30 are tobe communicated with other passages of honeycomb structural bodies,fitting of the other passages to the honeycomb structural body 30 orpiping can be favorably facilitated, because the end faces 37 and 39 areorthogonal to the curved central line.

(2) B--B end face

According to a second embodiment, a B--B end face and an E--E end faceof a honeycomb structural body are parallel to a floor face as shown inFIG. 3. In this embodiment, as shown in FIG. 4, since a lineperpendicularly drawn down from a centroid G of the honeycomb structuralbody 301 (see FIG. 3) falls in an area of the end face E--E, thehoneycomb structural body 301 is stably held on the floor face in anerected state. In addition, since the end face B--B is parallel to thefloor face, another honeycomb structural body having the same shape asthat of the honeycomb structural body 301 can be piled upon the end faceB--B of the honeycomb structural body 301 directly or indirectly througha mat.

(3) C--C end face

According to a third embodiment, as shown in FIG. 3, a C--C end face isorthogonal to an E--E end face. In this embodiment, as shown in FIG. 5,pipes can be fitted to the opposite ends of the honeycomb structuralbody 302 with the through holes 35 such that the pipes extends inorthogonal directions. This honeycomb structural body 302 functions as acoupling, and can be effectively utilized in a connecting portionbetween the orthogonal pipes, which saves installation space.

(4) D--D end face

According to a fourth embodiment, as shown in FIG. 3, the honeycombstructural body 303 is curved around the curving central line (axis O)substantially in the form of one-fourth circle. In this embodiment, asshown in FIG. 6, the honeycomb structural body has a one-fourth circularform in section, so that excellent pipe-fitting performance as attainedin case of the A--A end face and effective utilization in a reducedspace as attained in the case of the C--C end face can be both realized.

The outer wall configuration constituting the outermost peripheral wallof the honeycomb structural body according to the present invention mayhave any shape. For example, a round-section pipe 52 in FIG. 7(a), acollapsed round-section pipe 54 in FIG. 7(b), an elliptical-section pipe56 in FIG. 7(c), a square-section pipe 58 in FIG. 7(d), arectangular-section pipe 60 in FIG. 7(e), and a triangular-section pipe62 in FIG. 7(f) may be recited as a shape of the tubular outermostperipheral wall. As in the case with the honeycomb structural body shownin FIG. 2, a number of through holes are formed communicating betweenthe opposite end faces of the honeycomb structural body in the case ofthe honeycomb structural bodies in FIGS. 7(a) through 7(f). Thecross-sectional shape of the through holes is not necessarily limited toany shape, and for example, a square section, a rectangular section, atriangular section or a circular section may be employed for the shapeof the through holes.

The shapes of the curved honeycomb structural bodies may be varied invarious ways. For example, as shown in FIG. 8(a), the radius ofcurvature of a honeycomb structural body 100 is constant at R around acenter O, in which the lengths of the longest and shortest through holesare set at L1 and L2, respectively. As shown in FIG. 8(b), a curvedhoneycomb structural body 101 may be formed by connecting two curvedsections, one having a radius of curvature, R₁, with a center O₁ and theother having a radius of curvature, R2, with a center O₂. As shown inFIG. 8(c), a straight-line honeycomb structural body 102a may beconnected to a curved honeycomb structural body 102 having a radius ofcurvature R. Further, as shown in FIG. 8(d), honeycomb structural bodies103a mand 103b having different radii of curvature, R1 and R2, withcenters O₁ and O₂, respectively, are connected to each other through astraightline honeycomb structural body 103c. Furthermore, as shown inFIGS. 9(a), 9(b), 9(c) and 9(d), one or both of the opposite end facesof the honeycomb structural bodies may be inclined with respect to theextending direction of through holes (see honeycomb structural bodies104, 105, 106 and 107 in FIGS. 9(a) through (d)). In these embodiments,the inclined end faces are indicated by 104a, 104b, 105a, 105b, 106a,106b, 107a or 107d in FIGS. 9(a) through 9(d). In FIGS. 9(a) through(d), straight honeycomb structural bodies are denoted by 104c, 106c,107c or 107d. With respect to the radius of curvature and the curvingcenter in FIGS. 9(a) through 9(d), see FIGS. 8(a) through 8(d).

The honeycomb structural body according to the present invention may beproduced, for example, by the following method.

That is, a honeycomb structural body is extruded by using an ordinaryextruding die, and then placed on a receiving table having a curvedsurface with a given radius of curvature (such a curved surface mayinclude a plurality of curved portions). Thereby, the honeycombstructural body having an intended curved shape can be obtaining byordinary steps including firing.

In the following, experiments conducted for honeycomb structural bodieswill be explained.

Experiment 1

A vehicle in which an engine with a displacement of 2000 cc and ahoneycomb structural body as a catalyst carrier were mounted was runaccording to a running pattern shown in FIG. 10, and emission amounts ofcarbon monoxide CO, hydrocarbons HC and oxides of nitrogen NOx weremeasured. Results are shown in FIG. 11.

Honeycomb structural bodies made of a ceramic material and all having avolume of 1000 cc and a sectional shape shown in FIG. 8(a) were used ascatalyst carriers, and platinum Pt, rhodium Rh or paradium Pd wasemployed as a carried noble metal at an equal carried amount 1.4×10⁻³g/cm³. The outer wall constituting the outermost peripheral wallorthogonal to the extending direction of the through holes had anelliptical shape having a minor axis of 75 mm and a major axis of 100mm, and the cross-sectional shape of the through holes was square. Thenumber of the through holes was 60/cm² in a plane orthogonal to thepassing direction of the through holes. The thickness of the wallsbetween the adjacent through holes was 0.15 mm.

FIG. 11 shows experimental results, while the discharge amount of eachof CO, HC and NOx in the case of a conventional honeycomb structuralbody (that is, L1/L2=1) is taken as 1. When L1/L2 was not less than 0.8,the discharge amounts of CO, HC and NOx did not conspicuously decrease.When L1/L2 was not less than 1.2, the discharge amount of each of CO, HCand NOx decreased by not less than 10% as compared with the conventionalcase. Accordingly, L1/L2 is required to be not less than 0.8, andpreferably not less than 1.0, and more preferably not less than 1.2.

Experiment 2

An automobile engine having a displacement of 2000 cc was used, and ahoneycomb structural body was fitted midway an exhaust pipe. Thepressure loss of the honeycomb structural body was determined based on adifference in pressure between upstream and downstream the honeycombstructural body when the engine was operated at 40 km/hr. Results areshown in FIG. 12.

The honeycomb structural bodies used were made of a ceramic material(cordierite), and had shapes shown in FIGS. 9(a), 9(b), 9(c) or 9(d).The volume of every honeycomb structural body was 1800 cc. The outerwall constituted by the outermost peripheral wall had a circular shapewith a diameter of 100 mm as viewed in a plane orthogonal to the throughholes. The through holes had a square cross-sectional shape, and thenumber of the through holes was 90/cm² as viewed in a plane orthogonalto the through holes. The thickness of the walls between the adjacentthrough holes was 0.1 mm.

FIG. 12 shows results of the relationship between the radius ofcurvature and the pressure loss, while the pressure loss of theconventional honeycomb structural body was taken as 1. It is seen thatwhen the radius of curvature exceeds 100 mm, the pressure lossconspicuously decreases.

According to the above curved honeycomb structural bodies, as comparedwith the conventional straight-line honeycomb structural bodies, sincethe honeycomb structural bodies are curved, the honeycomb structuralbodies can be each arranged by effectively utilizing a narrow emptyportion of a space.

Further, when the honeycomb structural body according to the presentinvention is used to carry a catalyst, the catalyst unit can be arrangedby effectively utilizing a narrow space at a corner portion around anengine inside an engine room, which enhances the catalytic function forthe engine, saves the installation space in the engine room, reduce theweight of the constituent parts in the engine room, and effectivelyutilizes the space in the vehicle.

As having been explained above, according to the curved honeycombstructural bodies of the present invention, since the outer peripheralwall of the honeycomb structural body is curved, the honeycombstructural body can be excellently fitted in curved space or a curvedcorner portion, which has not been attained in the conventionalstraight-line honeycomb structural bodies.

Furthermore, according to the honeycomb structural body of the presentinvention, when the structural body is used as the catalyst carrier, anempty space inside the automobile engine room in which the engine ismounted can be utilized as effectively as possible, and furtherintegration of engine parts inside the engine room can be realized.

We claim:
 1. A honeycomb structural body including an outermostperipheral wall, and partition walls by which a number of through holesextending in an axial direction of the honeycomb structural body aredefined inside the outermost peripheral wall, said honeycomb structuralbody being bent around at least one line located in a directionorthogonal to an extending direction of said through holes andperpendicular to a first plane passing a center line of the honeycombstructural body, said center line being defined by continuouslyconnecting centroids of said outermost peripheral wall of the honeycombstructural body in respective planes orthogonal to the extendingdirection of the through holes thereof, wherein L1/L2 is no less than0.8, and R is not less than 100 mm, in which L1 is an axial length of alongest through hole among through holes located in an outer portion ofthe honeycomb structural body, L2 is an axial length of a shortestthrough hole among through holes located in an inner portion of thehoneycomb structural body, said axial length of the through hole being alength of the through hole as measured along a longitudinal center linethereof, and R is a radius of curvature of said center line of thehoneycomb structural body, said outer and inner portions of thehoneycomb structural body being located outside and inside a secondplane, respectively, said second plane passing said center line of thehoneycomb structural body and always extending in parallel to said atleast one line around which the honeycomb structural body is bent andperpendicular to said first plane.
 2. The honeycomb structural body setforth in claim 1, wherein the center line possesses at least twodifferent radii R of curvature.
 3. The honeycomb structural body setforth in claim 2, wherein centers of curves bent at at least twodifferent radii R of curvature are located on the same side of thehoneycomb structural body.
 4. The honeycomb structural body set forth inclaim 1, further comprising a straight-line portion in which saidthrough holes are not bent at at least one of an end portion of thehoneycomb structural body and at a portion other than said end portion.5. The honeycomb structural body set forth in claim 4, which is made ofa ceramic material.
 6. The honeycomb structural body set forth in claim4, wherein a catalyst is carried on inner walls defining the throughholes.
 7. The honeycomb structural body set forth in claim 1, which ismade of a ceramic material.
 8. The honeycomb structural body set forthin claim 7, wherein a catalyst is carried on inner walls defining thethrough holes.
 9. The honeycomb structural body set forth in claim 4,wherein a catalyst is carried on inner walls defining the through holes.10. The honeycomb structural body set forth in claim 1, wherein saidpartition walls extend in orthogonal directions as viewed in section atright angles to said extending direction of said through holes, therebydefining two orthogonal axes as viewed in said section, and said atleast one line is parallel to one of said two orthogonal axes.
 11. Thehoneycomb structural body set forth in claim 1, wherein a sectionalshape of the honeycomb structural body as viewed in section orthogonalto said extending direction of the through holes is one selected fromthe group consisting of a circular shape, an elliptical shape, an ovalshape, a square shape, a rectangular shape and a triangular shape.